revert: distinguish between "check" and "backup" strategy "check" behaves as backup did before. We check if the current file differs from destination and we create a backup if it does. This is used for untracked files that will be overwritten by formerly-deleted files. We have to do the manual check since no status output can provide the content comparison. "backup" is now doing unconditional backup. This can be used for files seen as modified compared to both the target and the working directory. In such a case, we know that the file differs from target without actually comparing any content. This new "backup" strategy will be especially useful in the case of files added between the target and the working directory -parent- with additional modifications in the working directory -itself-. In that case we know we need to back it up, but we cannot run the content check as the files does not exists in target.